300-410 Infrastructure Services Practice Question
A network administrator is configuring a Cisco IOS router to use NAT overload (PAT) for a small office. The inside network is 192.168.1.0/24, and the router's outside interface is GigabitEthernet0/0 with IP address 203.0.113.5. The administrator enters the following commands:
access-list 1 permit 192.168.1.0 0.0.0.255 ip nat inside source list 1 interface GigabitEthernet0/0 overload interface GigabitEthernet0/1 ip address 192.168.1.1 255.255.255.0 ip nat inside interface GigabitEthernet0/0 ip address 203.0.113.5 255.255.255.0 ip nat outside
However, hosts on the inside network cannot access the Internet. Which command is missing?
⚠ Common exam trap
The trap here is focusing on NAT configuration details when the actual problem is the absence of a default route, which is a common oversight in NAT troubleshooting.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
ip route 0.0.0.0 0.0.0.0 203.0.113.1
The NAT configuration correctly translates inside addresses to the outside interface address using PAT. However, the router lacks a default route to reach the Internet. Without a default route pointing to the ISP's next-hop address, the router cannot forward packets beyond its directly connected networks, so inside hosts cannot access external destinations.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
ip nat inside source list 1 pool overload
Why it's wrong here
This command would reference a NAT pool named 'overload', which does not exist. The current configuration uses interface overload, which is correct. Changing to a pool would require defining the pool first, but it would not fix the underlying issue. The missing element is a default route to direct outbound traffic to the ISP.
- ✗
ip nat inside source static 192.168.1.0 203.0.113.5
Why it's wrong here
A static NAT entry maps a single inside local address to a single inside global address. It does not provide overload (PAT) for multiple hosts and would conflict with the existing dynamic NAT configuration. The scenario requires dynamic PAT for the entire subnet, which is already configured with the 'overload' keyword. The missing piece is not a static mapping but a route or interface configuration.
- ✓
ip route 0.0.0.0 0.0.0.0 203.0.113.1
Why this is correct
The router needs a default route to forward traffic to the Internet. Without it, the router does not know where to send packets destined for outside networks. The NAT configuration only translates addresses; it does not provide routing. Adding a default route via the next-hop ISP router (203.0.113.1) enables the router to forward translated packets, allowing inside hosts to reach the Internet.
- ✗
ip nat pool overload 203.0.113.5 203.0.113.5 netmask 255.255.255.0
Why it's wrong here
The existing configuration uses interface overload, which is a valid method for PAT. Defining a NAT pool with a single address is unnecessary and would not resolve the connectivity issue. The problem is not with NAT translation but with routing. Without a default route, the router cannot forward packets to the Internet, regardless of NAT pool configuration.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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